Mac Pro losing Bluetooth when plugging in i-device

Ok folks, this is pretty obscure. I have a 2012 mac pro (purchased from refurb store) and it's been working fine for well over a year exept for an occasional issue.

I have a wired Apple keyboard and an Apple bluetooth trackpad. I used to have a short lightning cable (non-apple) plugged into the usb on the keyboard where I would charge/sync my iphone 5. I also have an Ipad 3 which I use a traditional cable plugged into a front usb port on the mac pro.

Occasionally when I would attach my ipad to the cable, I would lose my trackpad and sometimes the ipad would now be recognized by the system. I would have to power off the mac (press the button then press 'return' on the keyboard). Yes, the usb keyboard was still active (plugged into the rear of the mac pro).

I would have this problem using either of the front usb's. It didn't happen a lot but I did try to isolate by using different cables, trying to ground myself, the ipad and the cable. I will note that sometimes I hear a small static discharge (even though the speakers). It may be related to that, not sure.

The small non-apple cable failed so I am using a genuine apple lightning cable for my phone, also plugged into the front.

It now seems to be happening more frequent, on the iphone and/or the ipad, or even my ipad mini and ipod touch (lightning also).

in all cases, the only way to resolve is to power off the mac (or plug in a wired mouse to continue working). I wonder if this was the reason it was returned, re-certified and sold in the refurb store as it's pretty intermittent.

I have moved the lightning cable to the rear usb port and will run for a week or so like that to see if it's isolated to the front usb panel. I wonder if that's where the bluetooth gets it's 'usb' connectivity from.

Just wondering if anyone else has experienced this issue before I approach Apple on this (yes, I have applecare). Not looking forward to dragging this to the store for them to end up saying they found no issues.

BTW, I had a 2006 mac pro for 6 years, sitting in the same spot, and never had any issues with that (i am using the same keyboard/trackpad, never removed the new ones from the 2012 mp box).

Thanks!

Rick